Various foam dispensing devices have been proposed and used for mixing and expanding isocyanate, polyol and other foam components into polyurethane foam. When these components are mixed in proper proportions, they typically react quickly to form and solidify into an expanded foam. Component parts of the foam can also begin to solidify by reacting with moisture available in the air. Foam dispensing devices must, therefore, be kept free from buildup of the foam components and resulting expanded foam so that control valves and passageways do not become clogged, rendering the device inoperable and useless.
Certain prior foam dispensing devices required dismantling after each application in order to clean the dispenser. Most foam dispensers of recent design have utilized integral means for cleaning purposes, with a solvent being introduced to the dispenser after its use to flush the expanded foam and unreacted components therefrom. However, experience with apparatus of this general nature has shown that adequate cleaning is not always provided.
Other prior art dispensing devices, such as those disclosed in U.S. Pat. No. 4,469,251 to Sperry et al., and U.S. Pat. No. 4,399,930 to Harding, disclose the use of detachable, disposable mixing chambers. It does not appear, however, that these mixing chambers can be cleaned and reused if desired. Further, it does not appear that the design of these dispensers allows the substitution and use of mixing chambers of varying sizes.
The expanded foams generated by the foregoing apparatus are commonly used for insulation in, for example, refrigerator shells. Such shells require a fixed volume of foam --too much foam will split the shell; too little, and the shell will not be adequately insulated. The foam dispensing guns of the prior art, however, such as those disclosed in U.S. Pat. No. 4,469,251 to Sperry et al. and U.S. Pat. No. 4,399,930 to Harding, are not deemed to include sufficient means to enable a user to consistently dispense an identical volume of foam with each use of the dispenser.
The above-noted deficiencies were addressed in my U.S. Pat. No. 4,440,320, which is incorporated herein by reference. U.S. Pat. No. 4,440,320 discloses a foam dispensing apparatus having an improved valve arrangement for controlling the flow of the foam components through the dispenser so that the valves, passageways and the mixing chamber may be readily cleaned without disassembly, thus permitting the apparatus to be kept in operative condition at all times. The foam dispenser disclosed in my U.S. Pat. No. 4,440,320 also has a valve system which is capable of timed actuation, to allow only a predetermined amount of expanded foam to be produced.
To clean the foam dispenser disclosed in my U.S. Pat. No. 4,440,320, a solvent must be introduced into the dispenser after use to flush the expanded foam and unreacted components therefrom. Solvents useful for this purpose are generally toxic and/or flammable, and can pose both health and fire hazards in their use and disposal. These drawbacks make the use of a solvent undesirable to many users of foam dispensing apparatus.